The invention relates to a method for generating a stochastically alternating, pulsating, or cyclic flow of power or energy, for application to a power consuming device. This flow of power or energy can also be superimposed on another flow of power or energy.
In electrical machines, transformers, throttle coils, and capacitors that use cyclic power-electronic devices, German patent document DE 35 399 558 C2 teaches varying or sweeping the cyclic frequency at least in a specified frequency range in order to avoid undesirable emission of noise or electromagnetic noise spectra, especially when these systems and devices are located in a common chamber or body that can vibrate. By varying the cyclic frequency, the risk of excitation of the walls of the chamber or body by resonance can be significantly reduced, so that only insignificant noise is radiated, if any.
In an especially preferred arrangement, German patent document DE 35 39 558 C2 teaches the adaption of measures to detect the respective ambient conditions. In particular, other ambient noises are measured and analyzed, and the resultant spectral analysis is used to influence the variation of the frequency. In this manner, the noise emission has approximately the same spectrum as the background noise in the environment. As a result, the noises generated by the system or the individual device have a sound similar to the general background noise.
The swept cyclic frequency can be produced by connecting a noise generator through a lowpass filter and a voltage limiter that determines the frequency deviation to one input of an adder, whose second input is connected with a fixed voltage source that supplies the center frequency. A voltage-frequency converter is connected to the output of the adder so that the swept cyclic frequency can be tapped at the output of the converter. Alternatively, it is also possible to connect a random number generator and a fixed number generator having a larger bit number than the random number generator to separate inputs of an adder. The output of the adder influences a counter connected with a fixed-voltage generator that determines the counting limit, and the counter overflow of the counter on the output side corresponds to the swept cyclic frequency. The random number generator can be controlled as a function of a circuit for noise analysis.
The swept frequency produced in this manner is conducted as a cyclic frequency to devices and machines.
For controlling electrical positioning elements of proportional valves and the like, it is known to modulate the control signal with a higher frequency in order to cause the control element to perform a certain "chattering movement." As a result, although the influence of adhesive friction on the actuation of the control element can thus be reduced or eliminated, undesirable noises can develop.
The goal of the invention is to provide an improved method for supplying stochastically pulsating power to a power consuming device especially for electrohydraulic applications, specifically the supply of electric current to electromagnetic positioning elements of proportional valves.
This goal is achieved according to the invention by virtue of the fact that a noise signal that is superimposed on the power signal has a spectral amplitude or intensity distribution that is essentially the inverse of the amplitude frequency pattern of a noise parameter of the device or system. That is, the invention is based on the general idea of increasing the intensity of the noise in those frequency ranges in which the danger of disturbing resonant excitations is especially low (noise sensitive frequency ranges, as shown in FIG. 4) or which are located relatively far from resonant frequencies. Since the transmission of power or energy according to the invention is greater in those frequency ranges in which vibrations with only low amplitudes can be excited, an especially low-noise operation is made possible.